A novel stepwise dilution strategy to improve astaxanthin production of Haematococcus pluvialis in outdoor horizontal tubular photobioreactors

Abstract

The volume average light intensity in the photobioreactor (PBR) used for astaxanthin accumulation of Haematococcus pluvialis gradually decreased due to light attenuation caused by the accumulated biomass and astaxanthin. Excessive light intensity in the early stage of photoinduction resulted in photoinhibition while insufficient light intensity in the late stage limited the astaxanthin accumulation. In this study, the effect of dry cell weight on astaxanthin production was first investigated and the astaxanthin accumulation was improved by dilution. Based on this, a stepwise dilution strategy in the horizontal tubular photobioreactor (HTPBR) was developed to promote astaxanthin production and afterward verified in outdoor 16.5 m3 HTPBRs with 5-row parallel tubes. It was proved that twice diluting with an initial dry cell weight of 1 g L−1 in 3-row parallel tubes was the optima. By the stepwise dilution strategy, the astaxanthin content in algal cells and the astaxanthin productivity per dry heterotrophic cell weight increased from 2.56 % to 3.40 % and from 41.0 mg g−1 to 55.0 mg g−1, respectively. The gross profit was improved by 51.32 % by the easily operated stepwise dilution strategy.